1. Field of the Invention
This invention concerns an engine lubricating oil for diesel engines equipped with a particle filter in the exhaust gas stream and a process for operating a diesel engine with a particle filter system following the engine in the exhaust pipe, in which the temperature for the burning of particles deposited in the filter system is lowered because of the presence of catalytically active iron compounds.
2. Discussion of the Background
The emission of soot particles in the exhaust gas of diesel engines caused by their operation has already been subjected to more or less severe restrictions by legislation in various countries. The purpose of these restrictions is the most complete possible prevention of the emission into the atmosphere of particles containing soot, polycyclic compounds, and other substances generated from the operation of diesel engines.
For this reason, effective diesel particle filter systems have been developed by engineers, with so-called monolithic ceramic filters, with honeycomb structure ceramic bodies that contain channels sealed at alternate ends being used or ceramic spiral filters made of perforated steel support tubes arranged circularly with several layers of a roughened yarn of ceramic fibers (See ATV 1/2/88, pages 14 to 17).
The exhaust gas from the diesel engines flows through the labyrinthine passages of the monolithic ceramic filters, with the ceramic walls forming the honeycomb passageways in turn being porous and permitting the passage of the exhaust gas relieved of particles, or if flowing through the so-called spiral filter, with the exhaust gas particles being retained by the filaments of the ceramic yarn.
There is a corresponding pressure drop with increasing loading of these filter systems installed in the exhaust pipe downstream from the engine, which leads to an efficiency loss of the diesel engine. A pressure buildup in the exhaust gas system has to be avoided by continuous or periodic regeneration of the filter systems.
European Patent EP-No. 0 052 478-Bl discloses a method of operating a diesel engine in which a diesel fuel is burned in the engine, and then the engine exhaust gases are fed through a separator by which soot particles are removed from the gases. The separator is heated to a temperature high enough to bring about oxidation of the soot particles. Particles of a catalyst which lowers the oxidation temperature of the soot are introduced into the separator with the exhaust gases. Suitable catalyst substances are stated to be lead, copper, manganese, or mixtures of these, in elemental form or preferably in the form of chemical compounds, with the catalyst substances preferably being added to the diesel fuel.